“A gun-toting, cursing, former Amish female chief of police” stars in this excellent first in a new suspense series from romance veteran Castillo (Fade to Red ). When a serial killer strikes bucolic Painters Mill, Ohio, the killer’s signature—Roman numerals ritualistically carved into each victim’s abdomen—matches the MO of four unsolved murders from 16 years earlier. Police chief Kate Burkholder, who’s reluctant to dredge up the past, must keep secret that she knows why the old murders stopped. Not satisfied with the case’s progress, local politicos set up a multijurisdictional task force to assist, including a law-enforcement agent battling his own demons. The added scrutiny and the rising body count threaten to push the chief over the edge. Adept at creating characters with depth and nuance, Castillo smoothly integrates their backstories into a well-paced plot that illuminates the divide between the Amish and “English” worlds. (June)